Cell reversal diagnostics for a fuel cell stack

Abstract

A fuel cell reversal event is diagnosed by integrating current density via a controller in response to determine an accumulated charge density. The controller executes a control action when the accumulated charge density exceeds a threshold, including recording a diagnostic code indicative of event severity. The control action may include continuing stack operation at reduced power capability when the accumulated charge density exceeds a first threshold and shutting off the stack when the accumulated charge density exceeds a higher second threshold. The event may be detected by calculating a voltage difference between an average and a minimum cell voltage, and then determining if the difference exceeds a voltage difference threshold. The charge density thresholds may be adjusted based on age, state of health, and/or temperature of the fuel cell or stack. A fuel cell system includes the stack and controller.

What is claimed is: 
     
       1. A method for diagnosing a cell reversal event of a fuel cell in a fuel cell stack, the method comprising:
 detecting the cell reversal event via a controller; 
 integrating current density of the fuel cell over time in response to the detected cell reversal event, using the controller, to thereby determine an accumulated charge density; 
 comparing the accumulated charge density to a first calibrated charge density threshold and a second calibrated charge density threshold, the second calibrated charge density threshold being greater than the first calibrated charge density threshold; and 
 executing a control action with respect to the fuel cell stack when the accumulated charge density exceeds the first calibrated charge density threshold, including recording a diagnostic code in memory of the controller that is indicative of severity of the cell reversal event and temporarily continuing operation of the fuel cell stack at a reduced power capability when the accumulated charge density exceeds the first calibrated charge density threshold, and shutting off the fuel cell stack when the accumulated charge density exceeds the second charge density threshold. 
 
     
     
       2. The method of  claim 1 , wherein temporarily continuing operation of the fuel cell stack includes limiting current throughput of the fuel cell stack for a calibrated duration. 
     
     
       3. The method of  claim 1 , wherein temporarily continuing operation of the fuel cell stack includes increasing a flow of hydrogen to the fuel cell stack for a calibrated duration. 
     
     
       4. The method of  claim 1 , wherein detecting a cell reversal event includes calculating a voltage difference between an average cell voltage and a minimum cell voltage of the fuel cell, and thereafter determining whether the calculated voltage difference exceeds a voltage difference threshold. 
     
     
       5. The method of  claim 1 , further comprising: adjusting the first calibrated charge density threshold and/or the second calibrated charge density threshold via the controller based on an age or a state of health of the fuel cell or the fuel cell stack. 
     
     
       6. The method of  claim 1 , further comprising: adjusting the first calibrated charge density threshold and/or the second calibrated charge density threshold via the controller based on a temperature of the fuel cell or the fuel cell stack. 
     
     
       7. The method of  claim 1 , further comprising: using electricity from the fuel cell stack to energize drive wheels of a vehicle. 
     
     
       8. A fuel cell system comprising:
 a fuel cell stack having a plurality of fuel cells; and 
 a controller having a processor in communication with the plurality of fuel cells and programmed with instructions for diagnosing a cell reversal event, wherein execution of the instructions causes the controller to:
 detect the cell reversal event of one of the plurality of fuel cells; 
 integrate, over time, a current density of the fuel cell having the detected cell reversal event in response to detecting the cell reversal event, thereby determining an accumulated charge density; and 
 execute a control action with respect to the fuel cell stack when the accumulated charge density exceeds a first calibrated charge density threshold, including recording a diagnostic code, via the controller, that is indicative of severity of the cell reversal event, and continuing operation of the fuel cell stack at a reduced power capability when the accumulated charge density exceeds the first calibrated charge density threshold and is less than a second charge density threshold, and shutting off the fuel cell stack when the accumulated charge density exceeds the second charge density threshold. 
 
 
     
     
       9. The system of  claim 8 , wherein the controller is configured to temporarily continue operation of the fuel cell stack by limiting current throughput of the fuel cell stack for a calibrated duration. 
     
     
       10. The system of  claim 8 , wherein the controller is configured to temporarily continue operation of the fuel cell stack by increasing a flow of hydrogen to the fuel cell stack. 
     
     
       11. The system of  claim 8 , wherein the controller is configured to detect the cell reversal event by calculating a voltage difference between an average cell voltage and a minimum cell voltage of each of the fuel cells, and thereafter comparing the calculated difference to a threshold voltage difference. 
     
     
       12. The system of  claim 8 , wherein the controller is configured to automatically adjust the first calibrated charge density threshold and/or the second calibrated charge density threshold over time based on an age or state of health of the fuel cell or the fuel cell stack. 
     
     
       13. The system of  claim 8 , the system further comprising: at least one temperature sensor configured to measure a temperature of the fuel cell stack, wherein the controller is configured to automatically adjust the first calibrated charge density threshold and/or the second calibrated charge density threshold based on the measured temperature. 
     
     
       14. A vehicle comprising:
 a vehicle body; 
 a set of drive wheels positioned with respect to the vehicle body; and 
 a fuel cell system configured to deliver power to the drive wheels, the fuel cell system comprising:
 a fuel cell stack having a plurality of fuel cells; and 
 a controller having a processor in communication with the plurality of fuel cells and programmed with instructions for diagnosing a cell reversal event by calculating a voltage difference between an average cell voltage and a minimum cell voltage of each of the fuel cells, and comparing the calculated voltage difference to a threshold voltage difference, wherein execution of the instructions causes the controller to:
 detect the cell reversal event of one of the plurality of fuel cells; 
 integrate, over time, a current density of the fuel cell having the detected cell reversal event in response to detecting the cell reversal event, thereby determining an accumulated charge density; and 
 execute a control action with respect to the fuel cell stack when the accumulated charge density exceeds a first calibrated charge density threshold, including:
 recording a diagnostic code indicative of severity of the cell reversal event, and continuing operation of the fuel cell stack at a reduced power capability when the accumulated charge density exceeds the first charge density threshold; and 
 shutting off the fuel cell stack when the accumulated charge density exceeds a second charge density threshold that is greater than the first charge density threshold. 
 
 
 
 
     
     
       15. The vehicle of  claim 14 , wherein the controller is configured to temporarily continue operation of the fuel cell stack by limiting current throughput of the fuel cell stack for a calibrated duration and/or increasing a flow of hydrogen to the fuel cell stack. 
     
     
       16. The vehicle of  claim 14 , wherein the controller is configured to automatically adjust the first calibrated charge density threshold and/or the second calibrated charge density threshold over time based on an age or state of health of the fuel cell or the fuel cell stack. 
     
     
       17. The vehicle of  claim 14 , further comprising:
 at least one temperature sensor configured to measure a temperature of the fuel cell stack, wherein the controller is configured to automatically adjust the first calibrated charge density threshold and/or the second calibrated charge density threshold based on the measured temperature.